Drop obsolete annotations syntax

compiler/testData/psi/script/manyAnnotationsOnFile.kts

@@ -1,3 +1,3 @@
-[file: foo]
-[file:bar baz]
+@file:[ foo]
+@file:[bar baz]
 package bar

compiler/testData/psi/script/manyAnnotationsOnFile.txt

@@ -1,9 +1,10 @@
 JetFile: manyAnnotationsOnFile.kts
   FILE_ANNOTATION_LIST
     ANNOTATION
-      PsiElement(LBRACKET)('[')
+      PsiElement(AT)('@')
       PsiElement(file)('file')
       PsiElement(COLON)(':')
+      PsiElement(LBRACKET)('[')
       PsiWhiteSpace(' ')
       ANNOTATION_ENTRY
         CONSTRUCTOR_CALLEE
@@ -14,9 +15,10 @@ JetFile: manyAnnotationsOnFile.kts
       PsiElement(RBRACKET)(']')
     PsiWhiteSpace('\n')
     ANNOTATION
-      PsiElement(LBRACKET)('[')
+      PsiElement(AT)('@')
       PsiElement(file)('file')
       PsiElement(COLON)(':')
+      PsiElement(LBRACKET)('[')
       ANNOTATION_ENTRY
         CONSTRUCTOR_CALLEE
           TYPE_REFERENCE
@@ -41,4 +43,4 @@ JetFile: manyAnnotationsOnFile.kts
     <empty list>
   SCRIPT
     BLOCK
-      <empty list>
+      <empty list>